The present invention pertains to a system for facilitating an order change in the dry end conversion of a corrugated paperboard web. In particular, the invention relates to a method and apparatus for maintaining web continuity during an order change.
In a corrugator dry end, where a corrugated paperboard web is longitudinally scored and slit into multiple parallel output webs (or "outs"), the outs are directed through one or more downstream cut-off knives which cut the output webs into selected sheet lengths. When two cut-off knives are used, they are vertically separated and each is capable of cutting the full corrugator width web. A web selector positioned downstream of the slitter-scorer, divides the outs into two groups, one of which is directed to the upper cut-off knife and the other to the lower cut-off knife. Order changes must be effected while the upstream corrugator wet end continues to produce and deliver the continuous web to the slitter-scorer. An order change will typically result in a change in widths of the output webs, requiring redirection of at least a central portion of the web from one knife level to the other and possibly changes in edge trim widths as well.
The prior art has developed two basic order change systems for corrugator dry ends utilizing double level cut-off knives. One system is known as a gapless or plunge style order change system. In this system, there are two slitter-scorer stations immediately adjacent one another in the direction of web movement and through both of which the web travels. At order change, one slitter-scorer, operating on the currently running order, will lift out of operative engagement with the web, and the other slitter-scorer which is set to the new order alignment plunges down into operative engagement with the web. The result is a small order change region of corrugated web with overlapping slits and scores for both the running and the new orders.
Any gapless order change system must be able to accommodate redirection of the central portion of the web in the web selector device from one knife level to the other. In U.S. Pat. No. 5,496,431, a laterally adjustable cutting tool, positioned over the center of the web, makes a running diagonal cut to provide a smooth transition in the widths of the output webs directed to the upper and lower cut-off knives, allowing a repositioning of the web directing forks in the web selector device. In this system, the order change region of the web containing the diagonal connecting slit and the overlapping slit and score lines requires the use of separate diverters downstream of each of the upper and lower cut-off knives to divert the resultant scrap sheets. The diagonal pieces which are created by the system of this patent cannot be discharged in the usual manner onto the top of the stack, particularly when changing from a narrow web to a wide web on either knife level. The diagonal piece would fall off the top of the stack. Therefore, the system of this patent must have a diverter after each knife level.
In German Patent 44 25 155, the output webs exiting the slitter-scorer are simultaneously cut to chop out a scrap sheet containing the overlapping slits and scores from the running and new orders. The gap created by chopping out the scrap portion allows repositioning of the web directing forks at the web selector device. This system is not a true gapless order change, but does utilize pairs of alternately operable plunge cut slitter-scorers. This system also requires a separate rotary shear and a scrap sheet diverter between the slitter-scorer and the cut-off knife. In addition, because the scrapped out sheets may have many slits resulting in a limp and unstable sheet, they are difficult to divert and often result in jams.
The other type of order change system, a gap style order change system requires the use of a rotary shear located immediately downstream of the corrugator wet end. At order change, the rotary shear is operated to make a cross cut through the entire web. The downstream dry end equipment is accelerated to pull a gap between the tail edge of the running order and the leading edge of the new order defined by the shear cut. As the tail edge of the web passes through the slitter-scorer, the slitting and scoring tools can be repositioned in the gap and set for the new order. Alternately operable plunge cut slitter-scorers may also be used in a gap style order change. Similarly, as the trailing edge passes through the web selector device, it can be reset to change the direction of outs in the leading edge of the new order between the top and bottom cut-off knives.